North Korea has suspended access to the Kaesong industrial zone shared with the South – the latest move amid escalating tensions on the peninsula. South Korea’s defense minister warned that all options will be considered if worker safety is at risk.

South Korea’s Unification Ministry reports that 446 South Korean workers have been stranded at the facility, waiting to cross back into home territory since the early hours of Wednesday. Normally, daily entry clearance is given via telephone.

There are a total of about 860 South Korean workers in the Kaesong zone. One hundred and seventy-nine South Korean staff showed up at the border on Wednesday morning, but North Korea also refused to let them in.

North Korea could be making good on an earlier promise to close off the complex as part of the increasingly bellicose rhetoric exchanged between the two countries, also involving Washington.

In response South Korea’s Defense Minister Kim Kwan-jin said that all options are being considered, including military, if safety of South Koreans in the North is at risk, Reuters quoted Yonhap news agency as reporting.

South Korea claims to have contingency measures in place for dealing with hostage situations in Kaesong, but their administration is keeping silent on what those might be .

The Kaesong industrial zone is a jointly-operated facility established in the 2000s, and is considered to be among the major sources of income for the destitute North, as well as the only true joint venture between the warring neighbors.

The zone consists of 123 textile and other labor-intensive South Korean factories and generates US$92 million a year in wages for 53,400 North Koreans employed. The Kaesong project amounts to almost $2 billion a year in trade for North Korea, according to figures from South Korea.

Pyongyang has been ramping up its war rhetoric to mirror that of Washington and Seoul, following a third nuclear test in February, which provoked widespread condemnation and a fresh round of sanctions. The country’s young leader, Kim Jong-un has taken up office in December 2011.

Most experts share the belief that North Korea will confine its current actions to threats as it seemingly does not wish to incur the military wrath of those opposed to it, and that the young Kim simply wishes to cement his reputation as a solid ruler.

Interestingly, Kaesong was seen by some to represent the last vestiges of North-South cooperation. Speaking to RT just a few hours before the zone’s closing, investigative journalist Tim Shorrock explained that its importance to neighborly ties cannot be understated, and that its (then) ongoing operation was testament to the fact that Pyongyang did not want to consider a complete breakup in relations.

“The one thing to look for in Korea is the North-South industrial zone, called Kaesong. It’s still going. I call it the ‘Canary of the Korea’, like the canary in the coal mines… if that zone is still open, I think we still have some hope. As of this morning it was still going, which means that South Koreans by the thousands were going there to work, as well as North Koreans. So I have some optimism that there can be an accommodation here.”